This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application 2000-261929, filed on Aug. 30, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to a hydraulic brake apparatus for a vehicle. More particularly, the present invention pertains to a hydraulic brake apparatus for the vehicle having an auxiliary hydraulic pressure source for generating a power hydraulic pressure to be used to apply brake pressure to a wheel cylinder associated with a wheel of the vehicle in response to operation of a brake operating member, and a warning mechanism for informing of a failure of an outputted hydraulic pressure generated by the auxiliary hydraulic pressure source.
Various types of hydraulic brake apparatus for a vehicle are known. At least some known types of hydraulic brake apparatus include a master cylinder such as a hydraulic pressure generating apparatus for generating a brake pressure in response to operation of a brake operating member, and an auxiliary hydraulic pressure source for generating a power hydraulic pressure. The auxiliary hydraulic pressure source generally includes a hydraulic pump and an accumulator. These hydraulic brake apparatus typically require an adjustment of the power hydraulic pressure generated by the auxiliary hydraulic pressure source and an adequate warning in response to an excessive reduction of the power hydraulic pressure.
For example, U.S. Pat. No. 5,000,520 (corresponding to a Japanese Patent Application published on May 24, 1990 as Toku-Kai-Hei 2 (1990)-136365) discloses a hydraulic brake apparatus in which the power hydraulic pressure varies between 140-180 bar under operation of the auxiliary hydraulic pressure source. The pumping operation of a hydraulic pump is started in response to the reduction of the power hydraulic pressure below a predetermined lower limit and is continued until the power hydraulic pressure reaches an upper limit. A warning signal is generated in response to the reduction of the power hydraulic pressure below a predetermined lowest limit set at 105 bar.
In the apparatus disclosed in the above-mentioned U.S. patent, to operate the hydraulic pump and generate the warning signal when a relay contact fails, an electric circuit arrangement is provided that includes a pressure responsive switch and a relay arrangement for controlling operation of an electric driving motor connected to the hydraulic pump to maintain the power hydraulic pressure within a predetermined range (e.g. 140-180 bar), another pressure responsive switch for generating the warning signal in response to the reduction of the power hydraulic pressure below the predetermined lower limit, and another relay for controlling the operation of the electric driving motor.
In the apparatus described in the above-mentioned U.S. patent, if the hydraulic pump is normally operable, it is able to maintain a driving condition of the hydraulic pump in response to a reduction of the power hydraulic pressure. However, if the capacity of the accumulator is small, the warning signal may be frequently generated during normal operation of the hydraulic pump. Further, the electric circuit arrangement including the two pressure responsive switches and the two relays increases the manufacturing cost associated with the apparatus.
A need thus exists for a hydraulic brake apparatus having an auxiliary hydraulic pressure source for generating a power hydraulic pressure in which, if the hydraulic pump is normally operating, the operation of the hydraulic pump is controlled in response to varying the power hydraulic pressure to generate the power hydraulic pressure without generating frequent warning signals.
According to one aspect of the present invention, a hydraulic brake apparatus for a vehicle includes a reservoir containing brake fluid, a wheel cylinder associated with a road wheel of the vehicle, and an auxiliary hydraulic pressure source for generating a power hydraulic pressure that is used to apply brake pressure to the wheel cylinder in response to a braking requirement. The auxiliary hydraulic pressure source includes a hydraulic pump for increasing the pressure of the brake fluid supplied from the reservoir to generate the power hydraulic pressure. A power hydraulic pressure observing device observes continuously the power hydraulic pressure and generates a signal for controlling operation of the hydraulic pump based on the power hydraulic pressure. A pump operating condition judging mechanism judges whether or not the operating condition of the hydraulic pump satisfies a predetermined operating condition based on the power hydraulic pressure observed by the power hydraulic pressure observing means. A warning mechanism compares the power hydraulic pressure observed by the power hydraulic observing device with a predetermined hydraulic pressure and generates a warning signal indicating a failure of the power hydraulic pressure when the power hydraulic pressure is less than the predetermined hydraulic pressure and the pump operating condition judging mechanism judges that the operating condition of the hydraulic pump does not satisfy with the predetermined operating condition.
The pump operating condition judging mechanism detects a rising tendency of the power hydraulic pressure observed by the power hydraulic pressure observing device, and the pump operating condition judging mechanism judges that the operating condition of the hydraulic pump satisfies the predetermined operating condition when the power hydraulic pressure observed by the power hydraulic pressure observing device shows the rising tendency while the power hydraulic pressure observed by the power hydraulic pressure observing device is less than the predetermined hydraulic pressure.
The pump operating condition judging mechanism detects a rising tendency of the power hydraulic pressure observed by the power hydraulic pressure observing device and detects the starting of driving of the hydraulic pump, and the pump operating condition judging means judges that the operating condition of the hydraulic pump satisfies the predetermined operating condition when the power hydraulic pressure observed by the power hydraulic pressure observing device shows the rising tendency from a zero pressure within a predetermined time period after the driving of the hydraulic pump is started.
The pump operating condition judging mechanism detects a rising tendency of the power hydraulic pressure observed by the power hydraulic pressure observing device, and the pump operating condition judging mechanism judges that the operating condition of the hydraulic pump satisfies the predetermined operating condition when the power hydraulic pressure observed by the power hydraulic pressure observing device shows the rising tendency within the predetermined time period after the power hydraulic pressure observed by the power hydraulic pressure observing device falls below the predetermined hydraulic pressure.
The pump operating condition judging mechanism calculates a changing rate of the power hydraulic pressure observed by the power hydraulic pressure observing device and detects a starting of a driving of the hydraulic pump, and the pump operating condition judging mechanism judges that the operating condition of the hydraulic pump satisfies the predetermined operating condition when the changing rate of the power hydraulic pressure observed by the power hydraulic pressure observing device becomes a positive rate within a predetermined time period after the driving of the hydraulic pump is started.
The pump operating condition judging mechanism calculates a changing rate of the power hydraulic pressure observed by the power hydraulic pressure observing device, and the pump operating condition judging mechanism judges that the operating condition of the hydraulic pump satisfies the predetermined operating condition when the changing rate of the power hydraulic pressure observed by the power hydraulic pressure observing device changes from a negative rate to a positive rate within a predetermined time period after the power hydraulic pressure observed by the power hydraulic pressure observing device falls below the predetermined hydraulic pressure.
The hydraulic brake apparatus also includes a hydraulic pressure generating apparatus for generating the brake pressure in response to operation of a brake operating member. The hydraulic pressure generating apparatus includes a master cylinder and a hydraulic brake booster operable by the power hydraulic pressure to assist in operation of the master cylinder. A master cylinder hydraulic pressure sensor is provided to continuously detect the master cylinder hydraulic pressure generated by the master cylinder. A consumed hydraulic pressure estimating mechanism is provided for estimating a consumed hydraulic pressure at the auxiliary hydraulic pressure source based on the master cylinder pressure detected by the master cylinder hydraulic pressure sensor. The pump operating condition judging mechanism calculates a changing rate of the power hydraulic pressure observed by the power hydraulic pressure observing device and calculates a changing rate of the consumed hydraulic pressure estimated by the consumed hydraulic pressure estimating mechanism. The pump operating condition judging mechanism judges that the operating condition of the hydraulic pump satisfies the predetermined operating condition when a sum of the changing rate of the consumed hydraulic pressure estimated by the consumed hydraulic pressure estimating mechanism and a predetermined lowest changing rate of the outputting hydraulic pressure of the hydraulic pump is less than the changing rate of the power hydraulic pressure observed by the power hydraulic pressure observing device.
The hydraulic brake apparatus further includes a wheel cylinder hydraulic pressure sensor for detecting continuously the hydraulic brake pressure supplied to the wheel cylinder, a consumed hydraulic pressure estimating mechanism for estimating a consumed hydraulic pressure at the auxiliary hydraulic pressure source based on the wheel cylinder hydraulic detected by the wheel cylinder hydraulic pressure sensor. The pump operating condition judging mechanism calculates a changing rate of the power hydraulic pressure observed by the power hydraulic pressure observing device and calculates a changing rate of the consumed hydraulic pressure estimated by the consumed hydraulic pressure estimating mechanism. The pump operating condition judging mechanism judges that the operating condition of the hydraulic pump satisfies the predetermined operating condition when a sum of the changing rate of the consumed hydraulic pressure estimated by the consumed hydraulic pressure estimating mechanism and a predetermined lowest changing rate of the outputting hydraulic pressure of the hydraulic pump is less than the changing rate of the power hydraulic pressure observed by the power hydraulic pressure observing device.
According to another aspect of the present invention, a hydraulic brake apparatus for a vehicle includes a reservoir containing brake fluid, a wheel cylinder associated with a road wheel of the vehicle, and an auxiliary hydraulic pressure source for generating a power hydraulic pressure used to apply a brake pressure to the wheel cylinder in response to a braking requirement. The auxiliary hydraulic pressure source includes a hydraulic pump for increasing a pressure of the brake fluid supplied from the reservoir to generate the power hydraulic pressure. A power hydraulic pressure monitoring mechanism detects continuously the power hydraulic pressure and generates a signal for controlling operation of the hydraulic pump based on a detected power hydraulic pressure. A mechanism detects a changing rate of the power hydraulic pressure detected by the power hydraulic pressure monitoring mechanism, and generates a warning signal indicating a failure of the power hydraulic pressure on the basis of the detected power hydraulic pressure and the changing rate of the detected power hydraulic pressure.
According to another aspect of the invention, a method of operating a vehicle hydraulic brake apparatus involves continuously determining a power hydraulic pressure generated by an auxiliary hydraulic pressure source, wherein the auxiliary hydraulic pressure source includes a hydraulic pump which increases a pressure of brake fluid supplied from a reservoir to generate the power hydraulic pressure that is used to apply brake pressure to a vehicle wheel cylinder. A signal is generated to control operation of the hydraulic pump based on the power hydraulic pressure, and the power hydraulic pressure generated by the auxiliary hydraulic pressure source is compared with a predetermined hydraulic pressure of the auxiliary hydraulic pressure source. A determination is made regarding whether or not an operating condition of the hydraulic pump satisfies a predetermined operating condition based on the detected power hydraulic pressure, and a warning is issued indicating failure of the power hydraulic pressure when the detected power hydraulic pressure is less than the predetermined hydraulic pressure and when it is determined that the operating condition of the hydraulic pump does not satisfy the predetermined operating condition.